American diplomats are sending an uncompromising message to Arab states: those who do not support the planned United States operation against Saddam Hussein will be treated as enemies.

The warning is beginning to galvanise those who had been hoping that the threat of war would evaporate. "Many countries have been hiding their heads in the sand," said one Western official.

"Now there are the beginnings of a realisation that they must ensure they remain on the right side of the Americans."

The decision is toughest for the governments of Egypt and Jordan, who have stuck by their peace treaties with Israel in defiance of public opinion.

"They are sitting on the fence with both ears to the ground," said a diplomat in Tel-Aviv. "This is a very uncomfortable position which is impossible to hold for very long." Practically every Arab leader would be happy to see Saddam go if it could be done overnight.

"The problem is that it is not clear how this is going to be achieved, how long it will take, and who will replace him. Until they are sure of the result, no Arab country is ready to offer the Americans in public the use of its air bases.

There are signs that some in the Middle East are determined to be on the winning side, with a stake in fashioning the post-Saddam future of Iraq.

America, however, will have to clarify what diplomats call "the day after" issue. It was fears of Iraq splitting into three 'statelets' - and the effect that this would have on Saudi Arabia - that prevented Washington from toppling Saddam in 1991.

The Saudis, once the favoured ally of the US, are under intense pressure. Senior members of the royal family were sued by relatives of victims of the September 11 attacks for financing the al-Qa'eda network.

Al-Riyadh, a Saudi newspaper that reflects government thinking, has called on the kingdom to "reconsider US-Saudi strategic ties".

The Gulf war of 1991 was run from the Prince Sultan air base in Saudi Arabia, but that option is not available.

This puts the spotlight on the tiny emirate of Qatar, where the Americans are rushing to finish off a vast airbase at al-Udeid, with one of the longest runways in the Middle East.

When completed by the year's end, it will be able to hold 10,000 soldiers and 120 aircraft in hardened shelters designed to withstand biological or chemical attack.

Qatar is something of a maverick among Arab states, and would no doubt relish becoming Washington's favourite in the Middle East.

The emirate says it is against an attack on Iraq, but has made clear that it is open to persuasion if it has guarantees of Iraq's territorial unity.

Turkey, which borders northern Iraq, is hoping for a easing of its foreign debt in exchange for letting the Americans use its air bases.

As Ankara is determined to be in on any settlement that affects the Iraqi Kurds - Turkey has its own large Kurdish minority - there is little doubt that it will be an integral part of the US plans.

Israel is the only country in the Middle East actively pushing for speedy military action against Saddam. It has made clear that it will retaliate for any Iraqi Scuds that land on its soil.

The Arabs face a brutal choice. America's only allies in the region are non-Arab Turkey and Israel. If the Arab world is to be allowed at the top table of negotiations, it will have to put aside its concerns at Washington's humiliation of Iraq and adopt a policy of realpolitik.